This invention relates to a method for controlling changing-over of a rotational direction of an internal combustion engine, and more particularly to a method for controlling changing-over of a rotational speed of a spark-ignition internal combustion engine of the reciprocating piston type.
A vehicle such as a motor scooter, a snowmobile or the like which places importance on simplicity or convenience generally uses a small-sized two-cycle or four-cycle internal combustion engine as a drive source therefor. Also, in the vehicle, a stepless change gear of the centrifugal clutch type is typically used as a power transmission device for transmitting an output of the internal combustion engine to a driving wheel. Such a vehicle places importance on a decrease in size, a decrease in weight and a reduction in cost, so that a stepless change gear which does not include a backgear is typically used for this purpose.
A vehicle which uses a change gear including no backgear fails to move back; so that when it is required to reverse a travel direction of the vehicle in a narrow space, it is needed to lift the whole vehicle by hands. Thus, it is highly deteriorated in operability.
In order to permit a travel direction of the vehicle provided with no backgear to be reversed, it is required to change over or reverse a rotational direction of the internal combustion engine as required.
A method for changing over a rotational direction of an internal combustion engine is proposed in U.S. Pat. No. 5,036,802. The method proposed is so constructed that when it is required to change over a rotational direction of an internal combustion engine, operation of an ignition device is interrupted to deactivate the engine, to thereby reduce a rotational speed of a crank shaft of the engine; thus, ignition operation is carried a out at a sufficiently advanced rotation angle position to force piston back, resulting in a rotational direction of the engine being reversed, when the rotational speed of the crank shaft is reduced to a predetermined level to cause the engine to reach a state right before stopping. Immediately after a rotational direction of the engine is thus reversed, an ignition position of the engine is changed to a rotation angle position suitable for maintaining rotation of the engine in the reversed direction, so that operation of the engine is continued while keeping the rotational direction reversed.
The method proposed in the U.S. patent, as described above, deactivates the engine during a reduction in rotational speed of the engine, to thereby cause a large amount of unburnt gas mainly containing a hydrocarbon component to be discharged while reversing the rotational direction, leading to atmospheric pollution.
Also, the proposed method is constructed so as to restart ignition operation in a state that unburned exhaust gas remains in an exhaust pipe during reversing of a rotational direction of the engine. This causes afterfiring due to firing of the unburned gas in the exhaust pipe, leading to generation of explosive sound sufficient to give a driver anxiety and cause damage to the engine and exhaust pipe.